The present invention relates to a multi-scan type large screen display system with a pointer function.
The pointer function includes a function for showing a desired position on a large screen display. With a conventional optical overhead projector, the pointer function has been achieved by directly placing the front end of a pencil on a transparency sheet.
In recent years, a CRT projector display which can project a wide range of horizontal and vertical scanning frequencies has come to be utilized for presentations at meetings. As a pointer for the multi-scan type projector display, an optical laser pointer has been used but an electronic pointer has not existed. The optical laser pointer has been able to be used only when a single display unit is used in a room, but this pointer has been incompatible for displaying the same screen display that is displayed by using another display unit which is set in a separate room.
Even when using only one display unit in one room, it has been difficult for a presenter to manipulate the laser pointer with his hand because of an unavoidable movement of his hand.
FIG. 2 shows a general multi-scan type display system. In this drawing, 201, 202 and 203 denote separate kinds of computer signal source and their horizontal scanning frequencies are widely distributed from 30 kHz to 80 kHz. Numbers of their scanning lines are also different from each other.
204 designates a switcher and its input is connected to any one of these signal sources. 205 designates a multi-scan type display. The multi-scan type display 205 display the contents of the screen corresponding to each signal source. In setting vertical coordinates on the display screen, each computer sets them based on a respective total number of scanning lines. Since the vertical coordinates are different for each computer, it has been impossible to connect a common pointer generator.
In the meantime, manual input type PC (personal computers) having a fixed coordinates system have come to be sold at low prices in the market in recent years. According to the manual input type PC having a fixed coordinates system, it is possible to electronically display a pointer on an exclusive single scan type monitor which is attached to the computer. However, it has been difficult to superimpose an output signal of the manual input type PC on the large projector type display, because the horizontal frequency of the manual input type PC has been fixed to a low level of about 32 kHz while the horizontal scanning frequency of the originally intended input signal to the large screen display is variable in the range from about 30 kHz to 80 kHz. Accordingly, there has been no multi-scan type pointer function which can be applied to the multi-scan type projector display.
Generally, in a presentation system, it has been desired to dispose a compact flat panel monitor which can display the same contents as those displayed by the projector type display at the side of the presenter and make a display of the same pointer on the compact monitor. However, this has not been able to be realized because the normal compact flat panel monitor has been a single scan type.